The present invention relates, in general, to microlayer, multi-microlayer hybrid thermoplastic film structures and methods of making the same. More specifically, this invention relates to a multi-microlayer film having a degradable polymer layer and a thermoplastic elastomer layer.
Degradable polymers are widely used in a variety of different applications. These polymers are used in many different water-dispersible thermoformable articles, such as fibers, films and fabrics which maintain their integrity and strength when in use, but dissolve and disperse when placed in contact with large amounts of water. These fibers, films and fabrics are used in products such as personal care products, diapers, feminine napkins, wipes, incontinence products, release liners, product packaging, etc., which contain the above-mentioned fibers, films and fabrics.
Articles made from multi-layer films having a layer of a water or biologically degradable polymer are known. The other layers are typically polymers which lend structural support to the degradable polymer layer during use and provide a liquid barrier to help prevent premature degradation of the article.
However, multi-layer articles having a layer of a degradable polymer are relatively inflexible and do not offer a significant degree of breathability, making some articles uncomfortable to use for an extended period of time.
The prior art has attempted to provide articles which offer some degree of flexibility. This flexibility is in the form of elasticity of the article, which has been created by mixing an elastomeric resin with a polyolefin resin and using these blend compositions in films and articles. However, these films and articles do not offer significant breathability and are not generally water-dispersible.
Additionally, the prior art has provided a multi-layer film having a degradable elastomer layer and a degradable polymer layer. In particular, U.S. Pat. No. 5,391,421 discloses multi-layer films comprising biodegradable polymers. These films have only about 3-5 layers and are made by conventional techniques. Additionally, these films are not necessarily breathable, therefore causing articles made with these films to be uncomfortable to the wearer. Additionally, due to their high wet-state tensile strength, these films are difficult to flush down a conventional toilet since they do not readily disperse.
What is needed in the art is a flushable article having a multi-layer hybrid film which can offer significant breathability and offers elastomeric properties such that the film can be stretched when placed under a stretching force, but which returns to nearly its original shape when the stretching force is removed.
It is desired to provide a flushable multi-microlayer hybrid film that has elastomeric properties. Additionally, it is desired to provide a hybrid multi-microlayer film having a plurality of degradable polymer microlayers and a plurality of microlayers of a thermoplastic elastomer. Finally, it is desired to provide a nanoscale microlayer assembly of the multi-microlayer hybrid films which offer significant breathability while providing barrier protection against fluids and improved softness and comfort.
The present invention is directed to a multi-microlayer polymer film comprising a plurality of coextruded microlayers including a layer comprising an elastomeric, melt-extrudable polymer and a degradable layer comprising a water or biologically degradable, melt-extrudable polymer. The multi-microlayer film of this invention degrades in water for convenient disposability, but has sufficient strength and breathability for elastomeric use in applications such as disposable absorbent personal care products, garments, and other covering materials. Accordingly, the multi-microlayer polymer film of this invention, and products made with such film, can be easily disposed by flushing down a conventional toilet or drainage system.
One advantage of the multi-microlayer films of the present invention is that they offer a significant improvement in breathability over the prior art multi-layer films. The use of a plurality of microlayers enables films to be produced which permit water vapor produced by an individual to pass through the film and into the atmosphere. This enables the skin to stay drier and makes the film more comfortable to wear while helping to improve skin wellness.
Additionally, these hybrid films are designed to provide a high barrier against liquid penetration through the film. When these films are soaked in an excess amount of water, the films are designed to lose significant strength and toughness. The microlayer polymer film of this invention is particularly suitable for making personal care items such as diapers, feminine care products, adult incontinence products, and training pants, and health care products such as wound dressings or surgical gowns where a unique combination of the film-functional attributes such as softness, elastomeric behavior, water-response, and breathability are desired.
More particularly, the multi-microlayer polymer film of this invention includes a plurality of layers comprising the elastomeric, melt-extrudable polymer and a plurality of degradable layers comprising the water or biologically degradable, melt-extrudable polymer. The plurality of elastomeric layers and plurality of degradable layers are arranged in a series of parallel repeating laminate units, each laminate unit comprising at least one of the elastomeric layers and at least one of the degradable layers.
Generally, the individual microlayers of the film of this invention have a thickness small enough so that the elastomeric layers and the degradable layers of the microlayer film adhere to one another to form a laminate. Each microlayer in the polymer film of this invention has a thickness from about 10 angstroms to about 150 microns. Desirably, each microlayer has a thickness which does not exceed 50 microns and preferably does not exceed 10 microns. More particularly, each microlayer has a thickness which is not less than 100 angstroms and preferably not less than 500 angstroms. Broadly described, the film of this invention has degradable and elastomeric layers totaling about 8 to about 17,000 in number, and preferably about 60 to about 8000 in number. Thinner microlayer films, such as for personal care product covers, have a total of about 60 to about 4000 degradable and elastomeric microlayers. Preferably, such film has about 120 to about 1000 degradable and elastomeric microlayers.
According to a particular embodiment of the present invention, each laminate unit of the multi-microlayer film can include a tie layer positioned between the elastomeric layer and the degradable layer for modifying or enhancing properties of the microlayer film. The tie layer can be formed from a variety of polymers. Suitable polymers are chosen depending on the desired properties of the microlayer film. For example, the tie layer polymer can be selected to have an affinity to the elastomeric layer or the degradable layer or both for improving adhesion and interaction between those layers. The tie layer polymer can also be selected to enhance other properties of the microlayer film such as toughness and barrier.
According to another aspect of this invention, a method for making a multi-microlayer polymer film is provided. This method includes coextruding an elastomeric, melt-extrudable polymer and a degradable, melt-extrudable polymer to form a laminate comprising an elastomeric layer including the elastomeric, melt-extrudable polymer and a degradable layer including a degradable, melt-extrudable polymer. The method further includes separating the laminate while the laminate is in a melt-extrudable state to form a pair of laminate halves each including a portion of the elastomeric layer and a portion of the degradable layer. After separation, the laminate halves are thinned and widened and then stacked on top of one another to reform the laminate so that the laminate comprises a plurality of repeating laminate units in parallel stacking arrangement. Each laminate unit comprises an elastomeric layer including the elastomeric, melt-extrudable polymer and a degradable layer including the degradable, melt-extrudable polymer. The steps of separating, thinning and widening, and stacking are repeated to form the laminate into the multi-microlayer polymer film. The resulting microlayer film can also be stretched uniaxially or biaxially and thinned to reduce the basis weight of the microlayer film, enhance access of water and other aqueous liquids into the laminate structure of the microlayer film, enhance disintegration of the microlayer film in water, and enhance the water vapor transport rate or breathability of the film.